Superhard constructions &amp; methods of making same

ABSTRACT

A polycrystalline super hard construction comprises a body of polycrystalline super hard material and a substrate bonded to the body along an interface. The substrate a first end surface forming the interface, the first end surface comprising a projection extending from the body of the substrate into the body of super hard material towards the cutting face, the body of polycrystalline material extending around the projection. The body of polycrystalline material comprises a first region more thermally stable than a second region, the first region comprising an annular portion located around the projection, the second region extending between and bonding the first region to the substrate. The first region has a thickness from the cutting face along the peripheral side edge to the interface of at least around 3 mm and a portion of the projection has a thickness measured in a plane extending along the longitudinal axis of at least around 3 mm.

FIELD

This disclosure relates to superhard constructions and methods of makingsuch constructions, particularly but not exclusively to constructionscomprising polycrystalline diamond (PCD) structures attached to asubstrate, and tools comprising the same, particularly but notexclusively for use in rock degradation or drilling, or for boring intothe earth.

BACKGROUND

Polycrystalline superhard materials, such as polycrystalline diamond(PCD) and polycrystalline cubic boron nitride (PCBN) may be used in awide variety of tools for cutting, machining, drilling or degrading hardor abrasive materials such as rock, metal, ceramics, composites andwood-containing materials. In particular, tool inserts in the form ofcutting elements comprising PCD material are widely used in drill bitsfor boring into the earth to extract oil or gas. The working life ofsuper hard tool inserts may be limited by fracture of the super hardmaterial, including by spalling and chipping, or by wear of the toolinsert.

Cutting elements such as those for use in rock drill bits or othercutting tools typically have a body in the form of a substrate which hasan interface end/surface and a super hard material which forms a cuttinglayer bonded to the interface surface of the substrate by, for example,a sintering process. The substrate is generally formed of a tungstencarbide-cobalt alloy, sometimes referred to as cemented tungsten carbideand the super hard material layer is typically polycrystalline diamond(PCD), polycrystalline cubic boron nitride (PCBN) or a thermally stableproduct TSP material such as thermally stable polycrystalline diamond,the superhard layer bonded to the substrate in a PCD cutter elementtypically having a maximum thickness from the interface with thesubstrate to the working surface of around 2 mm.

Polycrystalline diamond (PCD) is an example of a superhard material(also called a superabrasive material or ultra hard material) comprisinga mass of substantially inter-grown diamond grains, forming a skeletalmass defining interstices between the diamond grains. PCD materialtypically comprises at least about 80 volume % of diamond and isconventionally made by subjecting an aggregated mass of diamond grainsto an ultra-high pressure of greater than about 5 GPa, and temperatureof at least about 1,200° C., for example. A material wholly or partlyfilling the interstices may be referred to as filler or binder material.

PCD is typically formed in the presence of a sintering aid such ascobalt, which promotes the inter-growth of diamond grains. Suitablesintering aids for PCD are also commonly referred to as asolvent-catalyst material for diamond, owing to their function ofdissolving, to some extent, the diamond and catalysing itsre-precipitation. A solvent-catalyst for diamond is understood be amaterial that is capable of promoting the growth of diamond or thedirect diamond-to-diamond inter-growth between diamond grains at apressure and temperature condition at which diamond is thermodynamicallystable. Consequently the interstices within the sintered PCD product maybe wholly or partially filled with residual solvent-catalyst material.Most typically, PCD is often formed on a cobalt-cemented tungstencarbide substrate, which provides a source of cobalt solvent-catalystfor the PCD. Materials that do not promote substantial coherentintergrowth between the diamond grains may themselves form strong bondswith diamond grains, but are not suitable solvent-catalysts for PCDsintering.

Cemented tungsten carbide which may be used to form a suitable substrateis formed from carbide particles being dispersed in a cobalt matrix bymixing tungsten carbide particles/grains and cobalt together thenheating to solidify. To form the cutting element with a superhardmaterial layer such as PCD or PCBN, diamond particles or grains or CBNgrains are placed adjacent the cemented tungsten carbide body in arefractory metal enclosure such as a niobium enclosure and are subjectedto high pressure and high temperature so that inter-grain bondingbetween the diamond grains or CBN grains occurs, forming apolycrystalline superhard diamond or polycrystalline CBN layer.

In some instances, the substrate may be fully cured prior to attachmentto the superhard material layer whereas in other cases, the substratemay be green, that is, not fully cured. In the latter case, thesubstrate may fully cure during the HTHP sintering process. Thesubstrate may be in powder form and may solidify during the sinteringprocess used to sinter the superhard material layer.

Ever increasing drives for improved productivity in the earth boringfield place ever increasing demands on the materials used for cuttingrock. Specifically, PCD materials with improved abrasion and impactresistance are required to achieve faster cut rates and longer toollife.

Cutting elements or tool inserts comprising PCD material are widely usedin drill bits for boring into the earth in the oil and gas drillingindustry. Rock drilling and other operations require high abrasionresistance and impact resistance. One of the factors limiting thesuccess of the polycrystalline diamond (PCD) abrasive cutters is thegeneration of heat due to friction between the PCD and the workmaterial. This heat causes the thermal degradation of the diamond layer.The thermal degradation increases the wear rate of the cutter throughincreased cracking and spalling of the PCD layer as well as backconversion of the diamond to graphite causing increased abrasive wear.

Methods used to improve the abrasion resistance of a PCD composite oftenresult in a decrease in impact resistance of the composite.

The most wear resistant grades of PCD and PCBN used in cutters usuallyfail by spalling resulting in a catastrophic fracture of the cutterbefore it has worn out. Spalling is considered to be caused by a crackpropagating from working area to the top free surface of the cuttingtool. During the use of these cutters, cracks grow until they reach acritical length at which catastrophic failure occurs, namely, when alarge portion of the PCD or PCBN breaks away in a brittle manner.Catastrophic failure of a component or structure indicates that a crackgrew to reach the “critical crack length” of the given structuralmaterial. The “critical crack length” is the acceptable length of crackbeyond which the propagation of the crack becomes uncontrollable leadingto catastrophic failure independently of the remaining non-working areaof the component. The long, fast growing cracks encountered during useof conventionally sintered PCD and PCBN can therefore result in shortertool life.

Furthermore, despite their high strength, polycrystalline diamond (PCD)and PCBN materials are usually susceptible to impact fracture due totheir low fracture toughness. Improving fracture toughness withoutadversely affecting the material's high strength and abrasion resistanceis a challenging task.

There is therefore a need for a superhard composite that has good orimproved abrasion, fracture and impact resistance and a method offorming such composites.

SUMMARY

Viewed from a first aspect there is provided a polycrystalline superhardconstruction comprising:

-   -   a body of polycrystalline superhard material having a cutting        face and a cutting edge; and    -   a substrate bonded to the body of polycrystalline superhard        material along an interface;    -   the construction having a central longitudinal axis extending        therethrough and a peripheral side edge; wherein:    -   the substrate comprises a substrate body and a first end surface        forming the interface, the first end surface of the substrate        comprising a projection extending from the body of the substrate        into the body of superhard material towards the cutting face,        the body of polycrystalline material extending around the        projection;    -   wherein the body of polycrystalline material comprises a first        region and a second region, the first region being more        thermally stable than the second region, the first region        comprising an annular portion located around the projection        extending from the body of the substrate, the cutting edge being        in the first region, the second region extending between and        bonding the first region to the substrate at one or more        locations; and    -   wherein the first region body of polycrystalline material has a        thickness from the cutting face along the peripheral side edge        to the interface with the substrate of at least around 3 mm; and    -   wherein at least a portion of the projection has a thickness        measured in a plane extending along the longitudinal axis of the        construction of at least around 3 mm.

Viewed from a second aspect there is provided a method of forming asuperhard polycrystalline construction, comprising:

-   -   providing a first mass of particles or grains of superhard        material; admixing the first mass of particles or grains with a        binder material to form a first green body;    -   placing the first green body into a canister to form a first        pre-sinter assembly;    -   treating the first pre-sinter assembly in the presence of a        catalyst/solvent material for the superhard grains at an        ultra-high pressure of around 5.5 GPa or greater and a        temperature to sinter together the grains of superhard material        to form a first polycrystalline superhard construction;    -   processing the first polycrystalline superhard construction to        form a first thermally stable annular region;    -   preparing a second pre-sinter assembly comprising placing a        second mass of particles or grains of superhard material to form        a second polycrystalline superhard region in contact with a        pre-formed substrate and the first thermally stable annular        region, the pre-formed substrate having a longitudinal axis and        comprising a body portion and a projection, the projection        extending at least in part from the body portion by around 3 mm        or greater as measured in a plane parallel to the longitudinal        axis of the substrate;    -   treating the second pre-sinter assembly in the presence of a        catalyst/solvent material for the superhard grains at an        ultra-high pressure of around 5.5 GPa or greater and a        temperature to sinter together the second mass of grains of        superhard material to form the second region and bond the        substrate to the first and second regions of polycrystalline        superhard material; wherein the projection extends from the body        of the substrate into the body of superhard material towards a        cutting face, the body of polycrystalline material extending        around the projection; and wherein the body of polycrystalline        material has a thickness from the cutting face along a        peripheral side edge of the construction to the interface with        the substrate of at least around 3 mm, the cutting face being in        the first region.

Viewed from a further aspect there is provided a tool comprising thesuperhard polycrystalline construction defined above, the tool being forcutting, milling, grinding, drilling, earth boring, rock drilling orother abrasive applications.

The tool may comprise, for example, a drill bit for earth boring or rockdrilling, a rotary fixed-cutter bit for use in the oil and gas drillingindustry, or a rolling cone drill bit, a hole opening tool, anexpandable tool, a reamer or other earth boring tools.

Viewed from another aspect there is provided a drill bit or a cutter ora component therefor comprising the superhard polycrystallineconstruction defined above.

BRIEF DESCRIPTION OF THE DRAWINGS

Examples will now be described by way of example and with reference tothe accompanying drawings in which:

FIG. 1 is a perspective view of an example superhard cutter element fora drill bit for boring into the earth;

FIGS. 2a to 2k are schematic cross-sections of example superhard cutterelements with differing interfaces with and/or structural compositionsof the superhard body and substrate attached thereto;

FIG. 3a is a schematic cross-section through a conventional superhardcutter element showing wear into the substrate through use;

FIG. 3b is a schematic cross-section through an example superhard cutterelement showing wear remaining in the superhard body after use; and

FIG. 4 is a plot showing the results of a vertical borer test comparingtwo conventional leached PCD cutter elements, and an example PCD cutterelement.

The same references refer to the same general features in all thedrawings.

DESCRIPTION

As used herein, a “superhard material” is a material having a Vickershardness of at least about 28 GPa. Diamond and cubic boron nitride (cBN)material are examples of superhard materials.

As used herein, a “superhard construction” means a constructioncomprising a body of polycrystalline superhard material. In such aconstruction, a substrate may be attached thereto.

As used herein, polycrystalline diamond (PCD) is a type ofpolycrystalline superhard (PCS) material comprising a mass of diamondgrains, a substantial portion of which are directly inter-bonded witheach other and in which the content of diamond is at least about 80volume percent of the material. In one example of PCD material,interstices between the diamond grains may be at least partly filledwith a binder material comprising a catalyst for diamond. As usedherein, “interstices” or “interstitial regions” are regions between thediamond grains of PCD material. In examples of PCD material, intersticesor interstitial regions may be substantially or partially filled with amaterial other than diamond, or they may be substantially empty. PCDmaterial may comprise at least a region from which catalyst material hasbeen removed from the interstices, leaving interstitial voids betweenthe diamond grains.

A “catalyst material” for a superhard material is capable of promotingthe growth or sintering of the superhard material.

The term “substrate” as used herein means any substrate over which thesuperhard material layer is formed. For example, a “substrate” as usedherein may be a transition layer formed over another substrate.

As used herein, the term “integrally formed” means regions or parts areproduced contiguous with each other and are not separated by a differentkind of material.

Components comprising PCBN are used principally for machining metals.PCBN material comprises a sintered mass of cubic boron nitride (cBN)grains. The cBN content of PCBN materials may be at least about 40volume %. When the cBN content in the PCBN is at least about 70 volume %there may be substantial direct contact among the cBN grains. When thecBN content is in the range from about 40 volume % to about 60 volume %of the compact, then the extent of direct contact among the cBN grainsis limited. PCBN may be made by subjecting a mass of cBN particlestogether with a powdered matrix phase, to a temperature and pressure atwhich the cBN is thermodynamically more stable than the hexagonal formof boron nitride, hBN. PCBN is less wear resistant than PCD which maymake it suitable for different applications to that of PCD.

In a PCD construction as shown in FIG. 1, a cutting element 1 includes asubstrate 10 with a layer of superhard material 12 formed on thesubstrate 10. The substrate 10 may be formed of a hard material such ascemented tungsten carbide. The superhard material 12 may be, forexample, polycrystalline diamond (PCD), a thermally stable product suchas thermally stable PCD (TSP), or polycrystalline cubic boron nitride(PCBN). The cutting element 1 may be mounted into a bit body such as adrag bit body (not shown) and may be suitable, for example, for use as acutter insert for a drill bit for boring into the earth.

The exposed surface of the superhard material opposite the face whichforms the interface with the substrate, forms the cutting face 14 of thecutter element, that is, the surface which, along with its edge 16,performs the cutting in use.

At one end of the substrate 10 is an interface surface 18 that forms aninterface with the superhard material layer 12 which is attached theretoat this interface surface. As shown in the example of FIG. 1, thesubstrate 10 is generally cylindrical and has a peripheral top edge 20and a peripheral surface 22.

As used herein, a PCD or PCBN grade is a PCD or PCBN materialcharacterised in terms of the volume content and size of diamond grainsin the case of PCD or cBN grains in the case of PCBN, the volume contentof interstitial regions between the grains, and composition of materialthat may be present within the interstitial regions. A grade ofsuperhard material may be made by a process including providing anaggregate mass of superhard grains having a size distribution suitablefor the grade, optionally introducing catalyst material or additivematerial into the aggregate mass, and subjecting the aggregated mass inthe presence of a source of catalyst material for the superhard materialto a pressure and temperature at which the superhard grains are morethermodynamically stable than graphite (in the case of diamond) or hBN(in the case of CBN), and at which the catalyst material is molten.Under these conditions, molten catalyst material may infiltrate from thesource into the aggregated mass and is likely to promote directintergrowth between the diamond grains in a process of sintering, toform a polycrystalline superhard structure. The aggregate mass maycomprise loose superhard grains or superhard grains held together by abinder material. In the context of diamond, the diamond grains may benatural or synthesised diamond grains.

Different grades of superhard material such as polycrystalline diamondmay have different microstructures and different mechanical properties,such as elastic (or Young's) modulus E, modulus of elasticity,transverse rupture strength (TRS), toughness (such as so-called K₁Ctoughness), hardness, density and coefficient of thermal expansion(CTE). Different PCD grades may also perform differently in use. Forexample, the wear rate and fracture resistance of different PCD gradesmay be different.

In the context of PCD, the PCD grades may comprise interstitial regionsfilled with material comprising cobalt metal, which is an example ofcatalyst material for diamond.

The polycrystalline superhard structure 12 shown in the cutter elementof FIG. 1 may comprise, for example, one or more PCD grades.

FIGS. 2a to 2k are schematic cross-sections through eleven examples ofexample polycrystalline superhard cutter elements 1. The eleven examplesall comprise a substrate 10 extending to a distance t from the cuttingface 14 of the polycrystalline superhard structure 12, thepolycrystalline superhard structure 12 having a thickness h as measuredfrom the cutting face 14 of the polycrystalline superhard structure 12along the barrel 13 thereof to the interface with the substrate 10, thebarrel 13 being the peripheral side edge of the cutter element 1. Inthese examples shown in FIGS. 2a to 2 k, the thickness h is preferablygreater than or equal to around 4 mm. Furthermore, in these examples,the thickness t is preferably less than or equal to around 0.5 mm.

In some examples, and in particular those where a planar central section26 of the substrate extends to and forms part of the cutting face 14,the cutting face 14 or a portion thereof may be protected againsterosion, corrosion or chemical degradation by attaching or spraying forexample a layer of resistant polymer, oxide, paint, composite materials,onto the surface. The protective layer(s) may be formed duringpre-composite assembly and bonded on to the cutter surface during HPHTsintering. Alternatively, the protective layer(s) may be attached to thecutter surface after sintering and processing and adhered thereto bysurface interaction.

The eleven examples of FIGS. 2a to 2k differ in the shape of the endface of the substrate portion 10 which forms the interface 18 with thepolycrystalline superhard structure 12 and/or the structural compositionof the polycrystalline superhard structure 12.

In the examples of FIGS. 2a to 2 k, the polycrystalline superhardstructure 12 comprises a first region 40 and a second region 42. Thefirst region 40 comprises, for example, polycrystalline diamond fromwhich at least a portion of the residual catalyst has been removed frominterstitial spaces between the inter-bonded diamond grains. The firstregion 40 is generally annular in shape in that it extends around aprotruding central section 27 of the substrate 10. The first region 40is spaced from the substrate 10 at one or more locations by the secondregion 42. The second region 42 differs from the first region 40 in oneor more characteristics such as diamond grain size, hardness, impactresistance, and composition and may act as a buffer for the first region40 either in use or in formation of the superhard cutter element 1 tomanage residual stresses in the element 1. The second region 42 alsoassists in attachment of the first region 40 which is pre-formed andrendered thermally stable prior to construction of the superhard cutterelement 1, to bond the first region 40 to the substrate 10. The secondregion 42 may also act as a barrier to infiltration of catalyst-solventor other elements from the substrate during construction of the superhard cutter element 1.

In the examples shown in FIGS. 2a to 2 k, the polycrystalline super hardlayer 12 may extend over the substrate portion at the cutting face 14 upto the second region 42 and this may be advantageous as the substrate 10is thereby protected from chemical erosion and abrasion duringapplication and also from chemical attack in the event that the cutterelement 1 is subjected to a treatment such as acid leaching aftersintering.

In the example shown in FIG. 2 a, the end face of the substrate portion10 which forms the interface 18 has a planar, coaxially located centralsection 26 which, at the end face is circular in cross section having adiameter d. This planar section 26 forms the furthest point of theinterface 18 from the body of the substrate and is spaced from thecutting face 14 by a distance t along the longitudinal axis of thecutter element 1. The substrate 10 thereby comprises a truncated cone atthe interface end projecting from the body of the substrate andextending through the layer of superhard material towards the cuttingface 14. The diameter d of the planar central section 26 of thesubstrate which forms part of the interface 18 with the superhard layeris less than the diameter D of the cutter element 1. The surface 28 ofthe substrate extends from the peripheral edge of the planar centralsection 26 towards the peripheral side edge or barrel 13 of the cutterelement 1 at an angle of, for example, up to around 30 degrees to theplane parallel to the plane through which the longitudinal axis of thecutter element 1 extends. In some examples this angle may be up toaround 5 degrees.

In the example shown in FIG. 2 a, the surface 28 does not extend to thebarrel 13 of the cutter element 1 but is spaced therefrom by asubstantially planar portion 43. The first region 40 comprises asubstantially cylindrical ring around the second region 42 whichseparates the first region from the substrate 10 and also extends overthe planar central section 26.

In some examples, the length of the planar portion 43 may be, forexample, between about 0 to about 3 mm, and in some examples around 2 mmor less.

The example shown in FIG. 2b differs from that shown in FIG. 2a in thatthe planar portion 43 is replaced with a stepped portion 46 such thatthe surface 28 of the substrate extending from the peripheral edge ofthe planar central section 26 towards the peripheral side edge 13 of thecutter element 1 extends to a first planar portion 47, the first region40 extending from the peripheral edge 13 of the cutter element to thefree edge 48 of the first planar portion.

The example in FIG. 2c differs from that of FIG. 2a in that the secondregion 42 follows the contours of the substrate 10 at the interface 18such that it forms a barrier between the substrate 10 and the firstregion 40 across the interface 18 with the second region extending overthe planar portion 43, along the surface 28 and over the planar centralsection 26. The inner periphery of the annular first region 40 iscorrespondingly shaped to contact the second region along its surface.

The example in FIG. 2d differs from that of FIG. 2c in that the depth ofthe second region 42 that extends along the surface 28 is greater thanthat in FIG. 2 c.

The example in FIG. 2e differs from that of FIG. 2b in the innerperipheral shape of the first region 40 which contacts the second region42. In the example of FIG. 2 b, the inner peripheral shape of the firstregion 40 being such that the first region was generally cylindricalwith a central aperture therein encasing the first region about theprotruding central section 27 of the substrate 10, whereas in theexample of FIG. 2 e, the second region 42 is substantiallyfrustro-conical in shape with a central aperture therein the peripheralwalls of which contact and extend around the surface 28 of theprotruding central section 27 of the substrate 10. The inner peripheralshape of the first region 40 follows the contours of the frustro-conicalshape of the second region 42 around the protruding central section 27of the substrate 10.

In the example of FIG. 2 f, the second region 42 is substantiallyfrustro-conical in shape with the diameter of the second region formingpart of the cutting face 14 being greater than the diameter at the pointof intersection with the surface 28 of the protruding central section 27of the substrate 10 which extends through the second region 42. Afurther region 49 which may be of the same elemental composition as thatof the second region 42 extends from the point of intersection of thesecond region 42 with the surface 28 and forms a substantially planarregion 50 extending to the barrel 13.

The example in FIG. 2g differs from that of FIG. 2f in that the secondregion 42 has a truncated peak that extends over a part of thesubstantially planar region 50.

The example in FIG. 2h differs from that of FIG. 2b in that the secondregion 42 is substantially frustro-conical in shape having a truncatedpeak and with the diameter of the second region forming part of thecutting face 14 being greater than the diameter at the point ofintersection with the stepped portion 46. In this example, the surface28 of the substrate extends from the peripheral edge of the planarcentral section 26 towards the peripheral side edge 13 of the cutterelement 1 to a first planar portion 47, the first region 40 extendingfrom the peripheral edge 13 of the cutter element to the free edge 48 ofthe first planar portion.

In the example in FIG. 2 i, the first region 40 is substantiallytoroidal in shape extending around the protruding central section 27 ofthe substrate 10. The first region 40 is located in part in a recess 51in the planar portion 43 of the substrate. The second region 42 extendsto fill the space around the first region 40 and protruding centralsection 27 of the substrate 10 to form the substantially cylindricalouter shape of the polycrystalline superhard structure 12.

In the examples of FIGS. 2j and 2 k, rather than being substantiallyconical as in the examples of FIGS. 2a and 2 b, the inner peripheralsurface of the first region 40 is convexly curved from the cutting face14 towards the planar portion 43 of the first region. The second region42 fills the region between first region and the protruding centralsection 27 of the substrate 10 to form the substantially cylindricalouter shape of the polycrystalline superhard structure 12.

The example of FIG. 2k differs from that in FIG. 2j in that the firstregion is in direct contact with the substrate 10 along the planarsurface 43 from the barrel 13 to the base of a stepped portion 46. Thesecond region 42 extends and fills the region from the cutting face 14to the stepped portion 46 and the surface 28 of the protruding centralsection 27 of the substrate 10.

As mentioned above, in some examples, the second region 42 may differfrom the first region 40 in for example, that it may be comprised of,for example, a different grade of superhard material to that of thefirst region 40, and/or, it may be a different composition to the firstregion 40.

Multiple additional regions of different grain size and/or compositionmay be included in some examples. The first and second and/or anysubsequent regions may comprise a mixture of WC and diamond powders, amixture of cBN and diamond powders, a mixture of refractory metals andsuper-hard (such as W, V, Mo) material powders, or any combinationthereof. Whilst not wishing to be bound by a particular theory, it isbelieved that the second region 42, and any further regions such as thefurther region 48, adjacent to the substrate 10 may eliminate the suddenchange in CTE between the substrate and the superhard layer and therebyassist in inhibiting cracking and/or delamination of the sinteredsuperhard layer from the substrate by minimising residual stress betweenlayers of different compositions.

By forming the first region of thermally stable PCD, it may be possibleto control the leaching profile to suit the end application of thecutter element 1.

FIG. 3a is a schematic cross-section through a conventional PCD cutter57 formed of a substrate 58 attached to a layer of PCD material 59showing wear into the substrate 58 through use. It will be seen that thewear flat 60 has progressed through both the PCD layer 59 and thesubstrate 57.

FIG. 3b is a schematic cross-section through an example PCD cutterelement showing wear remaining in the PCD body after use. The cuttershown in FIG. 3a is that of FIG. 2c and it will be seen that the wearflat 60 is retained in the layer of superhard material 12 and does notextend into the substrate 10 attached thereto.

Thus examples may enable the wear scar surface of the cutter to bemaintained in the layer of superhard material which is advantageous asthe wear scar surface may thereby be composed of homogeneous materialand hence provide uniform friction across the wear scar surface. Havingheterogeneous material across the wear scar surface as in theconventional cutter shown in FIG. 3a will result in the wear scarsurface being formed of materials having different coefficients offriction which may contribute to crack initiation near the wear scarleading to reduced performance of the cutter and increasedsusceptibility of the cutter to failure through spalling.

FIG. 4 is a plot showing the results of a vertical borer test comparingtwo conventional leached PCD cutter elements, and an example PCD cutterelement.

The grains of superhard material forming the first region 40 and/or thesecond region 42 may be, for example, diamond grains or particles, orfor example, cBN grains or particles. In the starting mixture prior tosintering they may be, for example, bimodal, that is, the feed comprisesa mixture of a coarse fraction of superhard grains and a fine fractionof superhard grains. In some examples, the coarse fraction may have, forexample, an average particle/grain size ranging from about 10 to 60microns. By “average particle or grain size” it is meant that theindividual particles/grains have a range of sizes with the meanparticle/grain size representing the “average”. The averageparticle/grain size of the fine fraction is less than the size of thecoarse fraction, for example between around 1/10 to 6/10 of the size ofthe coarse fraction, and may, in some examples, range for examplebetween about 0.1 to 20 microns.

In some examples, the weight ratio of the coarse fraction to the finefraction ranges from about 50% to about 97% coarse superhard grains andthe weight ratio of the fine fraction may be from about 3% to about 50%.In other examples, the weight ratio of the coarse fraction to the finefraction will range from about 70:30 to about 90:10.

In further examples, the weight ratio of the coarse fraction to the finefraction may range for example from about 60:40 to about 80:20.

In some examples, the particle size distributions of the coarse and finefractions do not overlap and in some examples the different sizecomponents of the compact are separated by an order of magnitude betweenthe separate size fractions making up the multimodal distribution.

Some examples consist of a wide bi-modal size distribution between thecoarse and fine fractions of superhard material, but some examples mayinclude three or even four or more size modes which may, for example, beseparated in size by an order of magnitude, for example, a blend ofparticle sizes whose average particle size is 20 microns, 2 microns, 200nm and 20 nm.

Sizing of diamond particles/grains into fine fraction, coarse fraction,or other sizes in between, may be through known processes such asjet-milling of larger diamond grains and the like.

In some examples, the average grain size of the superhard grains in thesecond region 42 is greater (ie the material is coarser) than theaverage grain size of the superhard grains in the first region 40.

In examples where the super hard material is polycrystalline diamondmaterial, the diamond grains used to form the polycrystalline diamondmaterial may be natural or synthetic.

In some examples, the polycrystalline super hard material is PCBN andthe superhard particles or grains comprise cBN.

In some examples, the binder catalyst/solvent used to assist in thebonding of the grains of superhard material such as diamond grains, maycomprise cobalt or some other iron group elements, such as iron ornickel, or an alloy thereof. Carbides, nitrides, borides, and oxides ofthe metals of Groups IV-VI in the periodic table are other examples ofnon-diamond material that might be added to the sinter mix. In someexamples, the binder/catalyst/sintering aid may be Co.

The cemented metal carbide substrate may be conventional in compositionand, thus, may be include any of the Group IVB, VB, or VIB metals, whichare pressed and sintered in the presence of a binder of cobalt, nickelor iron, or alloys thereof. In some examples, the metal carbide istungsten carbide. The cutter of FIGS. 1 to 2 k may be fabricated, forexample, as follows.

As used herein, a “green body” is a body comprising grains to besintered and a means of holding the grains together, such as a binder,for example an organic binder.

The substrate 10 is preferably pre-formed. In some examples, thesubstrate may be pre-formed by pressing the green body of grains of hardmaterial such as tungsten carbide into the desired shape, including theinterface features at one free end thereof, and sintering the green bodyto form the substrate element. In an alternative example, the substrateinterface features may be machined from a sintered cylindrical body ofhard material, to form the desired geometry for the interface features.The substrate may, for example, comprise WC particles bonded with acatalyst material such as cobalt, nickel, or iron, or mixtures thereof.

In some examples, the substrate may be cemented tungsten carbide. Insome examples, the cemented carbide substrate may be formed of tungstencarbide particles bonded together by a binder material comprising Co oran alloy of Co, Ni and Cr. The tungsten carbide particles may form atleast 70 weight percent and at most 95 weight percent of the substrate.The binder material may comprise between about 10 to 50 wt. % Ni,between about 0.1 to 10 wt. % Cr, and the remainder weight percentcomprises Co.

To form the superhard first region 40, the superhard construction may bemade by a method of preparing a green body comprising grains orparticles of superhard material and a catalyst/binder material forpromoting the sintering of the superhard grains. The green body may bemade by combining the grains or particles with the binder/catalyst andforming them into a body having substantially the same generalcylindrical shape as that of the overall intended sintered body ofsuperhard material 12, and drying the binder. At least some of thebinder material may be removed by, for example, burning it off. Thegreen body may be formed by a method including a compaction process, aninjection process or other methods such as molding, extrusion,deposition modelling methods.

The green body for the superhard construction for forming the firstregion 40 forms a pre-sinter assembly which may be encapsulated in acapsule for an ultra-high pressure furnace, as is known in the art. Inparticular, the superabrasive particles, for example in powder form, areplaced inside a metal cup formed, for example, of niobium, tantalum, ortitanium. The pre-composite is then outgassed at about 1050 degrees C.The pre-composite is closed by placing a second cup at the other end andthe pre-composite is sealed by cold isostatic pressing or EB welding.The pre-composite is then sintered to form a sintered body of superhardmaterial.

In one example, the method may include loading the capsule comprisingthe pre-sinter assembly into a press and subjecting the green body to anultra-high pressure and a temperature at which the superhard material isthermodynamically stable to sinter the superhard grains. In someexamples, the green body may comprise diamond grains and the pressure towhich the assembly is subjected is at least about 5 GPa and thetemperature is at least about 1,300 degrees centigrade. In someexamples, the pressure to which the assembly may be subjected is around5.5-6 GPa, but in some examples it may be around 7.7 GPa or greater.Also, in some examples, the temperature used in the sintering processmay be in the range of around 1400 to around 1500 degrees C.

A version of the method may include making a diamond composite structureby means of a method disclosed, for example, in PCT applicationpublication number WO2009/128034 with the additional step of admixingwith the diamond grains, prior to sintering, catalyst material in theform of a metal binder such as 0 to 3 wt % cobalt. A powder blendcomprising diamond particles and the metal binder material, such ascobalt may be prepared by combining these particles and blending themtogether. An effective powder preparation technology may be used toblend the powders, such as wet or dry multi-directional mixing,planetary ball milling and high shear mixing with a homogenizer. In oneexample, the mean size of the diamond particles for forming the firstregion 40 may be from about 1 to at least about 50 microns and they maybe combined with other particles by mixing the powders or, in somecases, stirring the powders together by hand. In one version of themethod, precursor materials suitable for subsequent conversion intobinder material may be included in the powder blend, and in one versionof the method, metal binder material may be introduced in a formsuitable for infiltration into a green body. The powder blend may bedeposited in a die or mold and compacted to form a green body, forexample by uni-axial compaction or other compaction method, such as coldisostatic pressing (CIP). The green body may be subjected to a sinteringprocess known in the art to form a sintered article. In one version, themethod may include loading the capsule comprising a pre-sinter assemblyinto a press and subjecting the green body to an ultra-high pressure anda temperature at which the superhard material is thermodynamicallystable to sinter the superhard grains.

After sintering, the polycrystalline super hard constructions may beground to size and may include, if desired, a 45° chamfer ofapproximately 0.4 mm height on the body of polycrystalline super hardmaterial so produced.

In the example of PCD, the sintered article may be subjected to asubsequent treatment at a pressure and temperature at which diamond isthermally stable to convert some or all of the non-diamond carbon backinto diamond and produce a diamond composite structure. An ultra-highpressure furnace well known in the art of diamond synthesis may be usedand the pressure may be at least about 5.5 GPa and the temperature maybe at least about 1,250 degrees centigrade for the second sinteringprocess.

Once the polycrystalline material has been sintered, in some examples,the body is cut using conventional techniques such as EDM machining orlaser ablation to form the desired shape for the first region. The bodyof polycrystalline superhard material once shaped into the desired shapefor the first region 40 is then rendered more thermally stable by, forexample, subjecting the body to a conventional procedure such as acidleaching to remove residual binder/catalyst from the interstitial spacesbetween the inter-bonded grains of superhard material. In some examples,substantially all of the residual binder/catalyst is removed whilst inothers only one or more regions of the first region 40 are depleted ofresidual binder/catalyst, depending on the intended application of thecutter element into which the first region 40 is to be incorporated.

A further pre-composite comprising the pre-formed substrate and firstregion 40 is prepared with the loose particles or grains of superhardmaterial and any addition binder/catalyst to form the second region 42.A green body for the superhard construction, which comprises thepre-formed substrate, the superhard construction comprising the firstregion and the particles of superhard material to form the second region42 such as diamond particles or cubic boron nitride particles, may beplaced onto the substrate and around the first region 42, to form apre-sinter assembly which may be encapsulated in a capsule for anultra-high pressure furnace, as is known in the art. In particular, thesuperabrasive particles for forming the second region, for example inpowder form, are placed inside a metal cup formed, for example, ofniobium, tantalum, or titanium. The pre-formed substrate and firstregion are placed inside the cup and hydrostatically pressed into thesuperhard powder such that the requisite powder mass is pressed aroundthe interface features of the preformed carbide substrate and firstregion to form the pre-composite. The pre-composite is then outgassed atabout 1050 degrees C. The pre-composite is closed by placing a secondcup at the other end and the pre-composite is sealed by cold isostaticpressing or EB welding.

The pre-composite is then sintered to form the sintered body ofsuperhard material comprising the first and second regions bonded to thesubstrate along the interface therewith.

In one example, the method may include loading the capsule comprisingthe pre-sinter assembly into a press and subjecting the green body to anultra-high pressure and a temperature at which the superhard material isthermodynamically stable to sinter the superhard grains. In someexamples, the green body may comprise diamond grains and the pressure towhich the assembly is subjected is at least about 5 GPa and thetemperature is at least about 1,300 degrees centigrade. In someexamples, the pressure to which the assembly may be subjected is around5.5-6 GPa, but in some examples it may be around 7.7 GPa or greater.Also, in some examples, the temperature used in the sintering processmay be in the range of around 1400 to around 1500 degrees C.

In an alternative version of the method, to form the super hard firstregion 40, a first pre-formed substrate is provided having a substratebody and a first end surface forming the interface, the first endsurface of the substrate comprising a projection extending from the bodyof the substrate. An aggregated mass of diamond grains or grains ofsuper hard material to form the super hard first region 40 is placedaround the pre-formed substrate in the canister used for sintering andthe construction is sintered under conventional sintering conditions toform a super hard first region attached to a first substrate. Thesintered construction is removed from the canister and a chamfer appliedto the peripheral edge of the free surface of the super hard firstregion, the chamfer being, for example, up to around 15 degrees from thefree surface, for example around 12 degrees. The majority of the firstsubstrate is removed from the construction and discarded. For example, alaser technique may be used to remove the first substrate from the superhard first region at around 0.5 mm below the interface between thesubstrate and the first region. The super hard first region and anyresidual substrate may then be treated, for example using a conventionalacid leaching process to render the first region thermally stable andremove residual catalyst/binder and the remainder of the firstsubstrate. The thermally stable first region may then be attached to afurther pre-formed substrate in the manner described above in respect ofthe first described example. After attachment of the first thermallystable region to the further pre-formed substrate by sintering, theconstruction may be treated further to form the final desired outerdimensions, for example, the cutting surface may be planed to a levelsurface and outer peripheral surfaces finished to the desired dimensionsand/or polished.

The sintered end product as shown for example in FIGS. 2a -2 k,comprises at least three regions formed of the ring forming the firstregion 40 which is substantially non-re-infiltrated or only partiallyre-infiltrated with catalyst material during the second sintering stage,a sintered region of filling material infiltrated with a catalyst metalwhich forms the second region 42, and the substrate 10. Infiltration ofcatalyst material from the substrate 10 into the first region 40 duringthe second sintering stage may be minimised due to limited interfacearea between the first region 40 and the substrate 10, and/or due to thecomposition of the first region. For example interstitial pores in thefirst region may be filled with nano sized diamond or other ceramicparticles, such as Alumina, Zirconia, and/or Yttria to inhibit furtherinfiltration of catalyst material from the substrate into the firstregion 40. As the content of catalyst material in the first region whichforms the periphery and therefore cutting edge of the cutter 1, noadditional leaching of the cutter may be necessary after the secondsintering stage.

In a further example, the second sintering process to attach the firstthermally stable region 40 to the substrate 27, may causecatalyst/binder to infiltrate from the substrate 27 into an annularregion in a portion of the first region 40 to form first region havingone or more thermally stable annular regions separated by a lessthermally stable region into which catalyst/binder has infiltrated, theless thermally stable region being spaced from the cutting surface 14 bya more thermally stable region.

Examples are described in more detail below with reference to thefollowing example which is provided herein by way of illustration onlyand is not intended to be limiting.

Example 1

A mass of diamond powder is admixed with catalyst metal such as cobaltor mixtures of metal powders by wet ball milling in alcohol and dryingat 80° C. The dried admixed powders may contain, for example, betweenaround 15 to around 30% catalyst materials. The powder is placed in aniobium or titanium cup and pressed using a manual press or pill stationto achieve a density that enables introducing enough powder for therequired final weight for forming one or more unbacked PCD bodes to formthe first region 40. The powders are degassed at a temperature rangingfrom between around 900° C. to around 1100° C. under a pressure ofbetween around 10-5 mbar. The cup containing the degassed material isclosed using another niobium cup and sealed by cold isostatic pressingin oil tank. Alternatively, EB welding may be used to seal niobium ontotitanium cups. The sealed pre-composite is sintered in a High PressureHigh Temperature system at a pressure of between around 5 GPa to around8 GPa or greater at a temperature of between about 1300° C. to 2000° C.to form an intergrown PCD structure.

After sintering, the cup material is removed from the PCD structure by aconventional techniques such as sand blasting, grinding or leaching torecover the solid PCD structure. The solid piece of PCD material is cutinto discs of required thickness using, for example, an EDM technique.To form the desired shape of the first region 40, a small hole is madethrough the disc by spark drilling/plasma techniques to form a passagefor the EDM cutting wire. A portion of solid material is then removedfrom the disc to produce rings of desired inner geometries and diameterssuch as those shown in FIGS. 2 to 2 k. The inner peripheral surfaces ofthe first region 40 may be non-circular and non-planar.

One or more annuli forming one or more first regions are then renderedmore thermally stable by, for example, subjecting the rings to an acidleaching technique to remove residual binder/catalyst. For example, atleast fifty per cent by volume of the catalyst material may be removed,and the leached ring(s) washed in de-ionised water to remove catalystsalts adhered inside the interstitial pores of the PCD material.

The interstitial spaces in the leached PCD ring may be partially filledby infiltrating nano size particles of one or more of, for example,diamond, alumina, zirconia, yttria or similar ceramics using method suchas filter vacuum, syringe, spraying or soaking in a boiling stabilisedsuspension of nano-sized particle slurry in water or alcohol.

The leached rings are then placed onto a pre-formed hard metal substrateinside a refractory metal cup such as a niobium or titanium cup. All orpart of the volume between the ring forming the first region 40 and thehard metal substrate 10 are filled with a powder to form the secondregion 42 once sintered. The powder may comprise, for example, one ormore different diamond grade materials, tungsten carbide, siliconcarbide, or non-catalyst metal powders and/or their mixtures.

The pre-composites are dried and degassed and sealed as described abovein respect of the formation of the first region 40. The sealed unit isthen sintered in an HPHT system. The HPHT pressure and temperature forthis second sintering cycle may not be the same as those used in themaking of the first region, for example, in forming the first region thesintering pressure may be 5.5 GPa and sintering temperature may be 1400°C., whereas for the second sintering process to form the final cutterelement, the sintering pressure may be, for example, 6.8 GPa andsintering temperature around 1500° C. In another example, the firstsintering pressure was 7.1 GPa, and first sintering temperature around1400° C. then the conditions of the second HPHT were changed to sinterat a pressure of 5.5 GPa and temperature of 1400° C.

The second sintering stage creates the second region 42 ofpolycrystalline superhard material and bonds this region to the firstregion and substrate to form the cutter element 1.

Example 2

Instead of forming the first region by sintering a substantiallycylindrical block of polycrystalline superhard material that issubsequently shaped to the desired shape of the first region using laserablation or EDM techniques, the first region may be formed as follows.Diamond powder is admixed with catalyst metal or mixtures of metalpowders by wet ball milling in alcohol and drying at 80° C. In oneexample, the powder that was admixed contained a mixture of micron andsub-micron sized particles. The sub-micron particles were not in excessof 10 volume per cent of the diamond mix. The dried admixed powderscontained between around 15-30% catalyst material(s).

A green body with the desired geometry and dimensions for forming thefirst region 40 was prepared from the diamond powder mix. In one casethe powder was pressed to form a green body around a pre-sinteredtungsten carbide substrate coated with a fine zirconia layer to preventbonding between the solid PCD and the substrate during first sintering.The use of pre-shaped solid carbide, zirconia or alumina helps toachieve controlled geometries of the pre-shaped green body duringsintering. In another case the green body was formed by injectionmoulding or 3D printing having a circular or non-circular inner corecomposed of particles from non-bonding ceramics such as zirconia oralumina surrounded by an outer layer composed of diamond particles.These two parts may be manufactured separately then assembled into onegreen body.

The assembly of diamond green body and the pre-shaped core substrate wasplaced in a niobium or titanium cup. In another example, a diamondpowder mix was introduced in the metal cup and pressed around thepre-shaped substrate using a manual press or pill station to achieve adensity that enables the introduction of enough powder for the requiredfinal weight for the formation of the desired first region.

The binder materials used in forming the green body was removed byheating up to 700° C. in a controlled atmosphere to form apre-composite. The pre-composite was then degassed at a temperatureranging from between around 900° C. and around 1100° C. under a pressureof 10-5 mbar.

The cup containing the degassed material was closed using anotherniobium cup and sealed by cold isostatic pressing in an oil tank.Alternatively, EB welding may be used to seal niobium onto a titaniumcup. The sealed pre-composite was sintered in a High Pressure HighTemperature system at a pressure of between around 5 GPa to around 8 GPaat a temperature of between around 1300° C. to around 2000° C. to forman intergrown PCD structure.

After sintering the cup material was removed by sand blasting, grindingor leaching to recover the solid PCD product that was to form a firstregion of the cutter element. The substrate at the core of the sinteredproduct was removed by mechanical means (such as drilling) or chemicalleaching.

The solid piece of PCD was then cut into discs of required thicknessusing EDM machining. The pre-shaped ring(s) to form one or more firstregions were leached in an acid mixture to remove at least fifty percentby volume of the residual binder/catalyst material from interstitialspaces in the PCD material.

A leached ring was then placed onto a further hard metal substrateinside a refractory metal cup such as a niobium or titanium cup. All orpart of the volume between the ring and the hard metal substrate wasfilled with powder to form the second region in the cutter element. Thesintered [product was then created using the same procedure as describedabove in Example 1.

The PCD cutter was recovered, processed and analysed.

The results are discussed below with reference to FIG. 4.

Various sample of PCD material were prepared and analysed by subjectingthe samples to a number of tests. The results of these tests are shownin FIG. 4.

The PCD compact formed according to Example 1 was compared in a verticalboring mill test with two leached conventional polycrystalline diamondcutter elements formed of diamond grains having an average grain size of12 microns and which were sintered under pressures of around 5.5 GPa. Inthis test, the wear flat area was measured as a function of the numberof passes of the cutter element boring into the workpiece. The resultsobtained are illustrated graphically in FIG. 4. The results provide anindication of the total wear scar area plotted against cutting length.It will be seen that the PCD compact formed according to Example 1denoted by the reference numeral 74 was able to achieve a greatercutting length and smaller wear scar area than that occurring in both ofthe conventionally leached PCD compacts (denoted by reference numerals70 and 72) which were subjected to the same test for comparison.

Whilst not wishing to be bound by a particular theory, it is believedthat crack propagation may be controlled by introducing a material suchas that formed by the second region in combination with the protrudingpart of the substrate which may act to slow down the propagation rate ofa crack before the critical length of the crack is reached and henceavoid spalling of the non-working area of the superhard material. Theprotruding part of the substrate has a higher impact resistance comparedto the superabrasive first region, as has the second region in someexamples, and thereby act(s) to arrest the cracks to avoid spalling orcatastrophic failure during use of the cutter element.

The size and shape of the substrate features may be tailored to thefinal application of the superhard material. It is believed possible toimprove spalling resistance without significantly compromising theoverall abrasion resistance of the material, which is desirable for PCDand PCBN cutting tools.

The vertical borer test results of these engineered structures show aconsiderable increase in PCD cutting tool life compared to conventionalPCD, and with no degradation in abrasion resistance.

Observation of the wear scar development during testing showed thematerial's ability to generate large wear scars without exhibitingbrittle-type micro-fractures (e.g. spalling or chipping), leading to alonger tool life.

Thus, examples of, for example, a PCD material, may be formed having acombination of high abrasion and fracture performance.

The PCD element 10 described with reference to FIGS. 2a to 2k may notneed to be further processed after sintering. For example, there may beno need to subject the element 1 to additional leaching procedures toleach out residual catalyst material from between the diamond grains, asthe first region which may form the majority of the superhard body 12 isalready more thermally stable than when first sintered.

The PCD body in the structure of FIGS. 1 to 2 k comprising a PCDstructure bonded to a cemented carbide support body may be furtherfinished by, for example, grinding, to provide a PCD element which issubstantially cylindrical and having a substantially planar workingsurface, or a generally domed, pointed, rounded conical orfrusto-conical working surface. The PCD element may be suitable for usein, for example, a rotary shear (or drag) bit for boring into the earth,for a percussion drill bit or for a pick for mining or asphaltdegradation.

While various examples have been described with reference to a number ofexamples, those skilled in the art will understand that various changesmay be made and equivalents may be substituted for elements thereof andthat these examples are not intended to limit the particular examplesdisclosed.

1. A polycrystalline superhard construction comprising: a body ofpolycrystalline superhard material having a cutting face and a cuttingedge; and a substrate bonded to the body of polycrystalline superhardmaterial along an interface; the construction having a centrallongitudinal axis extending therethrough and a peripheral side edge;wherein: the substrate comprises a substrate body and a first endsurface forming the interface, the first end surface of the substratecomprising a projection extending from the body of the substrate intothe body of superhard material towards the cutting face, the body ofpolycrystalline material extending around the projection; wherein thebody of polycrystalline material comprises a first region and a secondregion, the first region being more thermally stable than the secondregion, the first region comprising an annular portion located aroundthe projection extending from the body of the substrate, the cuttingedge being in the first region, the second region extending between andbonding the first region to the substrate at one or more locations; andwherein the first region body of polycrystalline material has athickness from the cutting face along the peripheral side edge to theinterface with the substrate of at least around 3 mm; and wherein atleast a portion of the projection has a thickness measured in a planeextending along the longitudinal axis of the construction of at leastaround 3 mm.
 2. The polycrystalline superhard construction of claim 1,wherein the projection from the substrate extends to and forms part ofthe working face.
 3. The polycrystalline superhard construction of claim1 wherein the first region body of polycrystalline material has athickness from the cutting face along the peripheral side edge to theinterface with the substrate of at least around 4 mm; and at least aportion of the projection has a thickness measured in a plane extendingalong the longitudinal axis of the construction of at least around 4 mm.4. The polycrystalline superhard construction of claim 1, wherein thefirst region differs from the second region in one or morecharacteristics comprising one or more of average grain size ofsuperhard material, coefficient of thermal expansion, super hardmaterial grain size distribution, hardness, impact resistance, and superhard material composition.
 5. (canceled)
 6. The polycrystallinesuperhard construction of claim 1, wherein the second region has alarger average grain size of superhard grains than the first region. 7.(canceled)
 8. The polycrystalline superhard construction of claim 1,wherein the body of superhard material comprises polycrystalline diamondmaterial having interbonded diamond grains and interstices therebetween;and wherein at least a portion of the body of superhard material formingthe first region is substantially free of a catalyst material fordiamond.
 9. The polycrystalline superhard construction of claim 1,wherein the body of superhard material comprises polycrystalline diamondmaterial having interbonded diamond grains and interstices therebetween;and wherein at least 50 vol % of the body of superhard material formingthe first region is substantially free of a catalyst material fordiamond.
 10. The polycrystalline superhard construction of claim 1,wherein the projection from the substrate extends to a distance ofaround 0.5 mm or less from the cutting face. 11-15. (canceled)
 16. Thepolycrystalline superhard construction of claim 1, further comprising aprotective layer over at least a portion of the cutting face.
 17. Thepolycrystalline superhard construction of claim 16, wherein theprotective layer comprises any one or more of a polymer, an oxide,paint, or a composite material to protect the cutting face or a portionthereof from one or more of erosion, corrosion or chemical degradation.18. The polycrystalline superhard construction of claim 1, wherein thesecond region comprises one or more of a mixture of WC and diamondpowder(s), a mixture of cBN and diamond powder(s), and/or a mixture ofrefractory metal(s) and hard material powders, the hard material powderscomprising one or more of tungsten, vanadium or molybdenum.
 19. Thepolycrystalline superhard construction of claim 1, wherein theprojection is dome shaped.
 20. The polycrystalline superhardconstruction of claim 1, wherein the projection comprises a planarcentral portion spaced from the body of the substrate by aninterconnecting surface.
 21. The polycrystalline superhard constructionof claim 20, wherein the planar central portion has a circularcross-section.
 22. The polycrystalline superhard construction of claim20, wherein the interconnecting surface is concave.
 23. Thepolycrystalline superhard construction of claim 22, wherein theinterconnecting surface extends from the planar central section to theperipheral side edge of the construction.
 24. The polycrystallinesuperhard construction of claim 23, wherein the projection isfrusto-conical in shape.
 25. The polycrystalline superhard constructionof claim 20, wherein the interconnecting surface comprises a firstportion extending from the planar central section to a position spacedfrom the peripheral side edge of the construction, the interconnectingsurface further comprising a second portion extending form the firstportion to the peripheral side edge, the projection being substantiallyfrusto-conical in shape.
 26. The polycrystalline superhard constructionof claim 25, wherein the second portion forms a shoulder portion havinga length of up to around 3 mm.
 27. The polycrystalline superhardconstruction of claim 25, wherein the projection has a peripheral outersurface inclined at an angle of up to around 30 degrees from the centrallongitudinal axis. 28-29. (canceled)
 30. A method of forming a superhardpolycrystalline construction, comprising: providing a first mass ofparticles or grains of superhard material; admixing the first mass ofparticles or grains with a binder material to form a first green body;placing the first green body into a canister to form a first pre-sinterassembly; treating the first pre-sinter assembly in the presence of acatalyst/solvent material for the superhard grains at an ultra-highpressure of around 5.5 GPa or greater and a temperature to sintertogether the grains of superhard material to form a firstpolycrystalline superhard construction; processing the firstpolycrystalline superhard construction to form a first thermally stableannular region; preparing a second pre-sinter assembly comprisingplacing a second mass of particles or grains of superhard material toform a second polycrystalline superhard region in contact with apre-formed substrate and the first thermally stable annular region, thepre-formed substrate having a longitudinal axis and comprising a bodyportion and a projection, the projection extending at least in part fromthe body portion by around 3 mm or greater as measured in a planeparallel to the longitudinal axis of the substrate; treating the secondpre-sinter assembly in the presence of a catalyst/solvent material forthe superhard grains at an ultra-high pressure of around 5.5 GPa orgreater and a temperature to sinter together the second: mass of grainsof superhard material to form the second region and bond the substrateto the first and second regions of polycrystalline superhard material;wherein the projection extends from the body of the substrate into thebody of superhard material towards a cutting face, the body ofpolycrystalline material extending around the projection; end whereinthe body of polycrystalline material has a thickness from the cuttingface along a peripheral side edge of the construction to the interfacewith the substrate of at least around 3 mm, the cutting face being inthe first region. 31-33. (canceled)
 34. The method of claim 30, whereinthe step of placing the first green body into a canister to form a firstpre-sinter assembly further comprises pressing the superhard particlesor grains around a pre-sintered shaped substrate, coated with a layerprevent bonding between the superhard particles and the substrate duringthe first sintering stage, the substrate being shaped to impart theannular shape to the superhard particles of grains once entered; andwherein the step of processing the first polycrystalline superhardconstruction to form a first annular region comprises removing theshaped substrate after sintering.
 35. The method of claim 34, whereinthe shaped substrate is coated with one or more of zirconia or alumina.36-45. (canceled)
 46. The method of claim 30, wherein the firstpolycrystalline super hard construction comprises a first substratehaving a substrate body and a projection extending from the body of thefirst substrate into the body of super hard material, the body ofpolycrystalline material extending around the projection and beingbonded to the first substrate along an interface; and wherein the bodyof polycrystalline material has a thickness from the cutting face alonga peripheral side edge of the construction to the Interface with thefirst substrate of at least around 3 mm; and wherein the step ofprocessing the first polycrystalline super hard construction to from thefirst thermally stable annular region comprises: removing at least apart of the first substrate from the first polycrystalline construction;treating the first polycrystalline construction to remove residualcatalyst/binder from the majority of interstitial spaces In the firstpolycrystalline construction and the residual first substrate. 47-55.(canceled)